Not Applicable
Not Applicable
This invention relates generally to the field of vascular occlusion devices and methods. More specifically, it relates to an apparatus and method for occluding a blood vessel by embolizing a targeted site (such as an aneurysm) in the blood vessel.
The embolization of blood vessels is desired in a number of clinical situations. For example, vascular embolization has been used to control vascular bleeding, to occlude the blood supply to tumors, and to occlude vascular aneurysms, particularly intracranial aneurysms. In recent years, vascular embolization for the treatment of aneurysms has received much attention. Several different treatment modalities have been employed in the prior art. U.S. Pat. No. 4,819,637xe2x80x94Dormandy, Jr. et al., for example, describes a vascular embolization system that employs a detachable balloon delivered to the aneurysm site by an intravascular catheter. The balloon is carried into the aneurysm at the tip of the catheter, and it is inflated inside the aneurysm with a solidifying fluid (typically a polymerizable resin or gel) to occlude the aneurysm. The balloon is then detached from the catheter by gentle traction on the catheter. While the balloon-type embolization device can provide an effective occlusion of many types of aneurysms, it is difficult to retrieve or move after the solidifying fluid sets, and it is difficult to visualize unless it is filled with a contrast material. Furthermore, there are risks of balloon rupture during inflation and of premature detachment of the balloon from the catheter.
Another approach is the direct injection of a liquid polymer embolic agent into the vascular site to be occluded. One type of liquid polymer used in the direct injection technique is a rapidly polymerizing liquid, such as a cyanoacrylate resin, particularly isobutyl cyanoacrylate, that is delivered to the target site as a liquid, and then is polymerized in situ. Alternatively, a liquid polymer that is precipitated at the target site from a carrier solution has been used. An example of this type of embolic agent is a cellulose acetate polymer mixed with bismuth trioxide and dissolved in dimethyl sulfoxide (DMSO). Another type is ethylene glycol copolymer dissolved in DMSO. On contact with blood, the DMSO diffuses out, and the polymer precipitates out and rapidly hardens into an embolic mass that conforms to the shape of the aneurysm. Other examples of materials used in this xe2x80x9cdirect injectionxe2x80x9d method are disclosed in the following U.S. Pat. No. 4,551,132xe2x80x94Pxc3xa1sztor et al.; U.S. Pat. No. 4,795,741xe2x80x94Leshchiner et al.; U.S. Pat. No. 5,525,334xe2x80x94Ito et al.; and U.S. Pat. No. 5,580,568xe2x80x94Greff et al.
The direct injection of liquid polymer embolic agents has proven difficult in practice. For example, migration of the polymeric material from the aneurysm and into the adjacent blood vessel has presented a problem. In addition, visualization of the embolization material requires that a contrasting agent be mixed with it, and selecting embolization materials and contrasting agents that are mutually compatible may result in performance compromises that are less than optimal. Furthermore, precise control of the deployment of the polymeric embolization material is difficult, leading to the risk of improper placement and/or premature solidification of the material. Moreover, once the embolization material is deployed and solidified, it is difficult to move or retrieve.
Another approach that has shown promise is the use of thrombogenic microcoils. These microcoils may be made of a biocompatible metal alloy (typically platinum and tungsten) or a suitable polymer. If made of metal, the coil may be provided with Dacron fibers to increase thrombogenicity. The coil is deployed through a microcatheter to the vascular site. Examples of microcoils are disclosed in the following U.S. Pat. No.: 4,994,069xe2x80x94Ritchart et al.; U.S. Pat. No. 5,122,136xe2x80x94Guglielmi et al.; U.S. Pat. No. 5,133,731xe2x80x94Butler et al.; U.S. Pat. No. 5,226,911xe2x80x94Chee et al.; U.S. Pat. No. 5,304,194xe2x80x94Chee et al.; U.S. Pat. No. 5,312,415xe2x80x94Palermo; U.S. Pat. No. 5,382,259xe2x80x94Phelps et al.; U.S. Pat. No. 5,382,260xe2x80x94Dormandy, Jr. et al.; U.S. Pat. No. 5,476,472xe2x80x94Dormandy, Jr. et al.; U.S. Pat. No. 5,578,074xe2x80x94Mirigian; U.S. Pat. No. 5,582,619xe2x80x94Ken; U.S. Pat. No. 5,624,461xe2x80x94Mariant; U.S. Pat. No. 5,639,277xe2x80x94Mariant et al.; U.S. Pat. No. 5,658,308xe2x80x94Snyder; U.S. Pat. No. 5,690,667xe2x80x94Gia; U.S. Pat. No. 5,690,671xe2x80x94McGurk et al.; U.S. Pat. No. 5,700,258xe2x80x94Mirigian et al.; U.S. Pat. No. 5,718,711xe2x80x94Berenstein et al.; U.S. Pat. No. 5,891,058xe2x80x94Taki et al.; U.S. Pat. No. 6,013,084xe2x80x94Ken et al.; U.S. Pat. No. 6,015,424xe2x80x94Rosenbluth et al.; and U.S. Pat. No. Des. 427,680xe2x80x94Mariant et al.
While many prior art microcoil devices have met with some success in treating small aneurysms with relatively narrow necks, it has been recognized that the most commonly used microcoil vaso-occlusive devices achieve less than satisfactory results in wide-necked aneurysms, particularly in the cerebrum. This has led to the development of threedimensional microcoil devices, such as those disclosed in U.S. Pat. No. 5,645,558xe2x80x94Horton; U.S. Pat. No. 5,911,731xe2x80x94Pham et al.; and U.S. Pat. No. 5,957,948xe2x80x94Mariant (the latter two being in a class of devices known as xe2x80x9cthree-dimensional Guglielmi detachable coilsxe2x80x9d, or xe2x80x9c3D-GDC""sxe2x80x9d). See, e.g., Tan et al., xe2x80x9cThe Feasibility of Three-Dimensional Guglielmi Detachable Coil for Embolisation of Wide Neck Cerebral Aneurysms,xe2x80x9d Interventional Neuroradiology, Vol. 6, pp. 53-57 (June, 2000); Cloft et al., xe2x80x9cUse of Three-Dimensional Guglielmi Detachable Coils in the Treatment of Wide-necked Cerebral Aneurysms,xe2x80x9d American Journal of Neuroradiology, Vol. 21, pp. 1312-1314 (August, 2000).
The typical three-dimensional microcoil is formed from a length of wire that is formed first into a primary configuration of a helical coil, and then into a secondary configuration that is one of a variety of three-dimensional shapes. The minimum energy state of this type of microcoil is its three-dimensional secondary configuration. When deployed inside an aneurysm, these devices assume a three-dimensional configuration, typically a somewhat spherical configuration, that is at or slightly greater than, the minimum energy state of the secondary configuration. Because the overall dimensions of these devices in their non-minimum energy state configuration is approximately equal to or smaller than the interior dimensions of the aneurysm, there is nothing to constrain the device from shifting or tumbling within the aneurysm due to blood flow dynamics.
In some of these three-dimensional devices (e.g., U.S. Pat. No. 5,122,136xe2x80x94Guglielmi et al.), the secondary configuration is itself a helix or some similar form that defines a longitudinal axis. Devices with what may be termed a xe2x80x9clongitudinalxe2x80x9d secondary configuration form a three-dimensional non-minimum energy state configuration when deployed inside an aneurysm, but, once deployed, they have displayed a tendency to revert to their minimum energy state configurations. This, in turn, results in compaction due to xe2x80x9ccoin stackingxe2x80x9d (i.e., returning to the secondary helical configuration), thereby allowing recanalization of the aneurysm.
There has thus been a long-felt, but as yet unsatisfied need for a microcoil vaso-occlusive device that has the advantages of many of the prior art microcoil devices, but that can be used effectively to treat aneurysms of many different sizes configurations, and in particular those with large neck widths. It would be advantageous for such a device to be compatible for use with existing guidewire and microcatheter microcoil delivery mechanisms, and to be capable of being manufactured at costs comparable with those of prior art microcoil devices.
Broadly, the present invention is a microcoil vaso-occlusive device that has a minimum energy state secondary configuration comprising a plurality of curved segments, each defining a discrete axis, whereby the device, in its minimum energy state configuration, defines multiple axes. More specifically, each segment defines a plane and an axis that is substantially perpendicular to the plane.
In a particular preferred embodiment, the present invention is an elongate microcoil structure having a minimum energy state secondary configuration that defines a plurality of tangentially-interconnected, substantially circular loops defining a plurality of separate axes. In one form of the preferred embodiment, the substantially circular closed loops are substantially coplanar and define axes that are substantially parallel. That is, the planes defined by the segments are themselves substantially coplanar. In another form of the preferred embodiment, each pair of adjacent loops defines a shallow angle, whereby their respective axes define an angle of not more than about 90xc2x0, and preferably not more than about 45xc2x0, between them.
In an alternative embodiment, the microcoil structure has a minimum energy state secondary configuration that defines a wave-form like structure comprising a longitudinal array of laterally-alternating open loops defining a plurality of separate axes. As in the preferred embodiment, the alternative embodiment may be in a first form in which the loops are substantially coplanar and their respective axes are substantially parallel, or in a second form in which each pair of adjacent loops defines a shallow angle, whereby their respective axes define an angle of not more than about 90xc2x0, and preferably not more than about 45xc2x0, between them.
In either embodiment, the device, in its minimum energy state secondary configuration, has a dimension that is substantially larger (preferably at least about 25% greater) than the largest dimension of the vascular space in which the device is to be deployed. Thus, when the device is deployed inside a vascular site such as an aneurysm, the confinement of the device within the site causes the device to assume a three-dimensional configuration that has a higher energy state than the minimum energy state. Because the minimum energy state of the device is larger (in at least one dimension) than the space in which it is deployed, the deployed device is constrained by its intimate contact with the walls of the aneurysm from returning to its minimum energy state configuration. Therefore, the device still engages the surrounding aneurysm wall surface, thereby minimizing shifting or tumbling due to blood flow dynamics. Furthermore, the minimum energy state secondary configuration (to which the device attempts to revert) is not one that is conducive to xe2x80x9ccoin stackingxe2x80x9d, thereby minimizing the degree of compaction that is experienced.
As will be better appreciated from the detailed description that follows, the present invention provides for effective embolization of vascular structures (particularly aneurysms) having a wide variety of shapes and sizes. It is especially advantageous for use in wide-necked aneurysms. Furthermore, as will be described in more detail below, the present invention may be deployed using conventional deployment mechanisms, such as microcatheters and guidewires.